Name: 巨型烏賊軸突如何改變神經科學 (How The Giant Squid Axon Changed Neuroscience)
Uploaded: 2024-08-01T07:45:19.000Z
Duration: 8 min 52 s

Scientists have been studying the brain and nervous system for hundreds of years.

數百年來，科學家們一直在研究大腦和神經系統。

Nowadays, scientists have all kinds of tricks and tools to study how the brain works.

如今，科學家們擁有各種研究大腦工作原理的技巧和工具。

We've got optogenetics and green glowing mice, and we've even mapped out every single synapse in the C. elegans nervous system.

我們已經有了光遺傳學和綠色發光小鼠，我們甚至繪製出了優雅小鼠神經系統的每一個突觸。

But all of those inventions are pretty new.

So what did the neuroscientists of yesteryear use instead?

那麼，昔日的神經科學家們用什麼來代替呢？

Yep, as wild as it sounds, scientists have actually learned a lot from... squid.

是的，雖然聽起來很瘋狂，但科學家們實際上已經從......烏賊身上學到了很多東西。

And, more specifically, the giant squid axon.

更確切地說，是巨型烏賊的軸突。

Now, just to clarify, I mean the giant squid axon, not the giant squid axon.

現在澄清一下，我指的是巨型烏賊軸突，而不是巨型魷魚軸突。

See, back in the mid-1900s, we didn't have all of those fancy tools to let us study brain activity.

要知道，在 20 世紀中期，我們還沒有這些先進的工具來研究大腦活動。

So scientists had to get creative when it came to figuring out how brains actually, you know, work.

是以，科學家們必鬚髮揮創造力，弄清楚大腦究竟是如何工作的。

At that time, options were pretty limited, because of course you couldn't just go digging around inside people's heads.

當時的選擇非常有限，因為你當然不可能去挖掘人們的內心世界。

Although doctors did perform a lot of lobotomies around that time.

儘管在那個年代，醫生們確實做了很多腦葉切除手術。

或者，你知道，以證據為基礎。

We were still relying on things like lesion studies to help us understand what different parts of the brain did.

我們仍然依賴於病變研究等方法來幫助我們瞭解大腦不同部分的功能。

And we didn't fully understand how, exactly, neurons send signals.

我們並不完全瞭解神經元究竟是如何發送信號的。

These days, we know that neurons send electrical signals called action potentials using ionic currents and pumps to change the electrical potential along the cell surface in the axons of neurons.

如今，我們知道神經元利用離子電流和泵，沿著神經元軸突的細胞表面改變電位，從而發出稱為動作電位的電信號。

What that means is that the inside of the neuron is more negative than the outside.

這意味著神經元內部比外部更消極。

There are more negative ions bumping around inside, which keeps the voltage at about negative 70 millivolts.

內部有更多的負離子在碰撞，從而使電壓保持在負 70 毫伏左右。

But when a neuron receives an incoming signal, that ionic balance gets disrupted, and the voltage starts to creep upward.

但當神經元接收到輸入信號時，離子平衡就會被打破，電壓就會開始上升。

Once it reaches the tipping point of about negative 55 millivolts, it sets off a cascade, throwing open the gated ion channels and causing the electrical potential to spike, thus creating the action potential.

一旦達到約負 55 毫伏的臨界點，它就會引發一系列連鎖反應，打開門控離子通道，導致電位驟升，從而產生動作電位。

This spike then travels along the axon, where it can push the axonal terminal to release chemicals called neurotransmitters, to pass the message on to the next neuron in the chain.

然後，尖峰沿著軸突移動，推動軸突末端釋放稱為神經遞質的化學物質，將資訊傳遞給鏈中的下一個神經元。

But when neuroscientists Alan Hodgkin and Andrew Huxley were first studying action potentials in the mid-1900s, they didn't have the tools necessary to measure these potentials in humans.

但是，當神經科學家艾倫-霍奇金（Alan Hodgkin）和安德魯-赫胥黎（Andrew Huxley）在 20 世紀中期首次研究動作電位時，他們還沒有測量人體動作電位所需的工具。

Instead, they chose to experiment with the longfin inshore, a small squid.

相反，他們選擇了長鰭近岸魷魚（一種小型魷魚）進行試驗。

Now, why in the world did they choose a squid instead of something less slimy and squishy?

現在，他們到底為什麼要選擇烏賊，而不是不那麼黏糊糊、軟綿綿的東西呢？

Although these creatures are only one to two feet long, so like that big, the giant axon measures up to 1.5 millimeters in diameter, which is about the diameter of this pipe cleaner, making it more than a thousand times wider than a typical human axon.

雖然這些生物只有一到兩英尺長，就像那麼大一樣，但巨型軸突的直徑卻高達 1.5 毫米，大約相當於這個水管清潔器的直徑，這使得它比典型的人類軸突寬 1000 多倍。

Why would a dinky little squid need such a huge axon?

為什麼小小的烏賊需要如此巨大的軸突？

Well, the axon connects to the water jet propulsion system, and in the wild, this allows the squid to rapidly escape from predators.

軸突連接著噴水推進系統，在野外，這使烏賊能夠迅速逃離捕食者。

Wide axons transmit electrical signals much faster than thin ones, as the added thickness allows a larger number of electrons to flow through at any given time.

寬軸突傳輸電信號的速度要比細軸突快得多，因為增加的厚度可以讓更多的電子在任何時間流過。

Humans can get around this limitation because we have myelination around most of our axons, which basically acts as insulation for the neurons and helps us transmit signals faster.

人類可以繞過這一限制，因為我們的大部分軸突周圍都有髓鞘，這基本上就像是神經元的絕緣體，幫助我們更快地傳輸信號。

Instead of myelin, squids just evolved an enormous axon.

魷魚只是進化出了一條巨大的軸突，而不是髓鞘。

After all, the faster they could escape, the more likely they were to survive and be able to pass on that trait to their offspring.

畢竟，它們逃得越快，就越有可能存活下來，並將這種特性傳給後代。

This wide axon of the longfin inshore squid made them the perfect model organism for studying action potentials, because you could easily insert a wire into the axon in order to measure the electrical potential.

長鰭近岸魷魚的這種寬軸突使它們成為研究動作電位的完美模式生物，因為你可以很容易地將一根導線插入軸突以測量電位。

Back in 1930, a dude named John Zachary Young was studying the nervous systems of sea creatures, pretty much any species he could get his hands on.

早在 1930 年，一個名叫約翰-扎卡里-楊的人就在研究海洋生物的神經系統，幾乎所有他能接觸到的物種都在研究之列。

And during his research, he realized that these long, stringy structures that had previously been mistaken for blood vessels were actually neurons.

在研究過程中，他發現這些以前被誤認為是血管的細長結構實際上是神經元。

A bit later, Hodgkin and Huxley came along and jabbed an electrode in it.

過了一會兒，霍奇金和赫胥黎走了過來，在它身上插了一根電極。

This allowed them to record the first ever action potential, the spike of a neuron sending a signal.

這使他們能夠記錄下有史以來的第一個動作電位，即神經元發出信號的尖峰。

To do this, they used technology called a voltage clamp.

為此，他們使用了一種名為電壓鉗的技術。

When an action potential shoots through the axon, sodium and potassium ions flow in and out of the cell pretty rapidly, depending on how the ion channels open and close.

當動作電位通過軸突時，鈉離子和鉀離子會迅速進出細胞，這取決於離子通道的開閉方式。

With the voltage clamp, Hodgkin and Huxley could measure how much current they needed to inject in order to keep the voltage constant while that process was happening.

有了電壓鉗，霍奇金和赫胥黎就可以測量他們需要注入多大的電流才能在這一過程中保持電壓恆定。

By doing so, they could track how much charge was flowing into and out of the cell at any given time.

通過這種方法，他們可以隨時跟蹤流入和流出電池的電荷量。

With this experimental strategy, they were able to see that the neuron first experiences depolarization, that spike I talked about earlier, and then hyperpolarization, where it actually overshoots the normal resting potential of negative 70 millivolts, dipping even lower down and creating a barrier that makes it just a little bit harder for the neuron to send another action potential and helping keep signals distinct.

通過這種實驗策略，他們能夠看到神經元首先經歷去極化，也就是我之前提到的尖峰，然後是超極化，在超極化過程中，神經元實際上超過了負 70 毫伏的正常靜息電位，甚至更低，並形成一個障礙，使神經元更難發出另一個動作電位，並幫助保持信號的獨特性。

But even though they could now see the shape of the action potential, they didn't actually know how the action potential was being formed.

但是，即使他們現在能看到動作電位的形狀，他們實際上並不知道動作電位是如何形成的。

That is, which ions were going where to create that quintessential spike.

也就是說，哪些離子去了哪裡，從而產生了典型的尖峰。

And obviously you can't just see ions, so testing it proved to be kind of a challenge.

顯然，你不能只看到離子，所以測試它是一項挑戰。

But Hodgkin and Huxley had another tool in their back pocket.

但是，霍奇金和赫胥黎的口袋裡還有一個工具。

They added chemicals called tetrodotoxin and tetraethylammonium to the solution they were keeping the squid axons in.

他們在保存烏賊軸突的溶液中添加了名為河豚毒素和四乙基銨的化學物質。

These compounds block sodium and potassium channels, respectively.

這些化合物分別阻斷鈉通道和鉀通道。

Fun fact, tetrodotoxin is the toxic compound produced by pufferfish and other poisonous sea creatures that makes them so deadly.

有趣的是，河豚毒素是河豚和其他有毒海洋生物產生的有毒化合物，使它們變得如此致命。

It blocks the sodium channels that allow your nerve cells to send their signals.

它能阻斷讓神經細胞發送信號的鈉通道。

If in fact you've consumed the venom of the blowfish, and from what the chef has told me it's quite probable, you have 24 hours to live. 24 hours?!

如果你真的吃了河豚的毒液，而且廚師告訴我這很有可能，那麼你只有 24 小時的生命。24小時？

By looking at the current when these channels were blocked, or when they removed sodium and potassium from the medium, Hodgkin and Huxley were able to figure out that sodium channels open first and cause the depolarization phase of the action potential, and that afterwards potassium channels open and the outward flow of potassium ions causes the hyperpolarization.

霍奇金和赫胥黎通過觀察這些通道被阻斷或從介質中移除鈉和鉀時的電流，發現鈉通道首先打開，導致動作電位的去極化階段，然後鉀通道打開，鉀離子外流導致超極化。

This discovery was a huge advance in helping us understand how neurons send action potentials, and how those action potentials could be controlled and manipulated for future experiments.

這一發現是一個巨大的進步，它幫助我們瞭解神經元如何發出動作電位，以及如何在未來的實驗中控制和操縱這些動作電位。

In fact, it won them the Nobel Prize in Physiology or Medicine in 1963.

事實上，這為他們贏得了 1963 年的諾貝爾生理學或醫學獎。

Though their choice of model organism may seem a bit strange, Hodgkin and Huxley made no mistake.

儘管他們選擇的模式生物似乎有點奇怪，但霍奇金和赫胥黎並沒有犯錯。

They found the perfect organism for the experiments they wanted to run, with just the right morphology to help us understand how our own nervous system functions.

他們發現了一種完美的生物體，這種生物體的形態正好可以幫助我們瞭解我們自身的神經系統是如何運作的。

Today, squids still play an important role in research, but they aren't the only sea scientists studying memory, and the African killifish has become an integral part of modern aging research.

如今，魷魚仍在研究中發揮著重要作用，但它們並不是唯一研究記憶的海洋科學家，非洲鱂魚已成為現代衰老研究中不可或缺的一部分。

So it's pretty clear that researchers can go beyond mice, worms, and flies when it comes to choosing animal models for studying the brain.

是以，研究人員在選擇研究大腦的動物模型時，顯然可以不侷限於小鼠、蠕蟲和蒼蠅。

I want to give a huge thank you to the International Youth Neuroscience Association for their help researching and writing the script for this video.

我要向國際青少年神經科學協會表示衷心的感謝，感謝他們幫助研究和編寫本視頻的腳本。

Founded at the 2016 International Brainbee, the IYNA is an next generation of neuroscientists.

IYNA 在 2016 年國際腦蜂大會上成立，是新一代的神經科學家。

They're a really cool organization, and I highly recommend checking them out if you're in high school or early on in college and love all this kind of stuff.

他們是一個很酷的組織，如果你是高中生或大學新生，又喜歡這類東西，我強烈建議你去看看。

To learn more about IYNA and how you can get involved, check out the link down below.

要了解有關 IYNA 的更多資訊以及如何參與其中，請點擊下面的鏈接。

Thanks for watching this episode of Neuro Transmissions.

感謝您收看本期《神經傳輸》。

Until our next transmission, I'm Alie Astrocyte.

在下次傳送之前，我是阿利-阿斯特羅賽特。